1. Field of the Invention
The present invention relates to an apparatus, such as an optical apparatus including binoculars, a camera including a digital camera and a video camera, and the like, and particularly relates to a drive mechanism, for example, for driving a lens and to a guide mechanism, for example, for guiding the lens, with which the apparatus is provided.
2. Description of the Related Arts
In the field of digital cameras, a more down-sized (i.e. miniaturized) and compact camera is desired in contrast with a conventional common camera. Meanwhile, as a drive mechanism for driving a lens used in the digital camera, there has been employed a cam mechanism as has been conventionally used in a common camera. That is, the digital camera has a construction in which a pin is fixed to a lens frame (or a movable frame), and in which a plurality of cam slots, engaging the same pin, are formed in a plurality of cylindrical members that engage and overlap one over the other. With the construction, a lens supported by the lens frame is driven in its optical axis.
However, even if one tries to downsize or miniaturize the cylindrical member having the cam slot and/or to downsize the pin engaging the cam slot, etc., there is a limitation to downsizing those components from a point of view of processing and/or assembling it. In other words, there arises a problem that the miniaturization of the cam mechanism can not catch up with the miniaturization of an optical system used therein.
Also, the cam mechanism is equipped with a tilt prevention mechanism for preventing a tilt of each lens advancing and retreating in its optical axis. With this arrangement, the movable frame for holding the lens advances and retreats while turning about the optical axis. Therefore, in case that one tries to miniaturize it while realizing a prevention of mutual interference of the plurality of movable frames, it is difficult to let a span of the tilt prevention mechanism be longer. As a result, a prevention of the tilt of the lens becomes difficult.
Furthermore, in the conventional cam mechanism, each lens is accommodated inside the cylindrical member. Therefore, it is difficult to perform the alignment of the optical system after assemblage thereof.
On the other hand, conventionally, a camera, video camera, digital camera, or the like, has had a guide mechanism for guiding a lens in a direction of an optical axis thereof at a time of moving the lens for zooming, focussing, etc. upon photographing. In the construction, there has been conventionally provided, for example, an MR (magnetic resistance) sensor for detecting a position of the lens that is driven in the optical direction, in order to control the position thereof. This MR sensor is a magnetic sensor, which is a magneto-resistive sensor having a characteristic that its resistance varies in a magnetic field when the intensity of the magnetic field varies. That is, the MR sensor moves in a longitudinal direction nearby a magnetized plate in which there are arranged a plurality of N- and S-poles alternately, with which arrangement the position of an object connected to the MR sensor is detected by reading the state of the magnetic field.
In this construction, in order to enhance an ability of the detection, it is necessary to ensure an accuracy of mutual location and mutual structures between the MR sensor and its counterpart magnetized plate. In this construction, a gap between a sensor surface of the MR sensor and the magnetized plate opposing the sensor surface thereof must be most strictly taken care of in order to ensure the accuracy thereof. However, the MR sensor and the magnetized plate are mounted on separated members moving relative to each other. Therefore, generally speaking, it is difficult to ensure the accuracy of the gap therebetween, only by the accuracy of components employed in the structure and/or by the accuracy of assemblage thereof.
In order to solve this technical problem, it has been practiced that, for example, a spacer or the like having a thickness corresponding to a required gap therebetween is inserted between the MR sensor and the magnetized plate, and that one of the MR sensor and the magnetized plate is brought into a press contact with the other thereof by means of a plate spring, or the like, by which the accuracy of the gap is ensured.
Meanwhile, in a type where the lens frame is hung down by a guide shaft, the lens frame is driven along the guide shaft in the direction of the optical axis. In this arrangement, however, it is necessary to restrict or prevent the turning of the lens frame around the guide shaft. In order to prevent the turning thereof, it has been practiced that an additional guide shaft is provided parallel to the foregoing guide shaft in which the additional guide shaft is fitted to a groove, or the like, that is additionally provided on the lens frame.
In this construction, in case that the optical performance thereof is considerably degraded due to swinging of the center of the optical axis of the lens frame, it is necessary to further suppress the play or looseness between the groove of the lens frame and the additional guide shaft, and the lens frame is biased on one side relative to the additional guide shaft by means of a spring, etc.
However, in the above construction, there are installed the detector for detecting the position of the lens and the mechanism for restricting or preventing the turning of the lens separately, in the guide mechanism for guiding the lens. This leads to an increment of the number of component parts and the number of assembling steps, which in turn incurs a large-sized apparatus and/or a high cost of production.
On the other hand, there has been conventionally provided, for example, a drive mechanism employing a piezoelectric element. The drive mechanism has a plurality of driving parts for linearly driving a plurality of lenses, for instance. With reference to FIG. 25 illustrating a drive mechanism for driving a lens in a camera, it is explained about the drive mechanism.
FIG. 25 is a perspective view of the drive mechanism for driving the lens. The lens drive mechanism has a lens frame 321a for holding a lens 300L1; a shaft bearing part 333a connected to the lens frame 321a; a guide shaft 328a, extending in a direction of the optical axis, slidably engaging the shaft bearing part 333a for guiding the lens frame 321a in the direction thereof; a lens frame 321b for holding a lens 300L2; a shaft bearing part 333b connected to the lens frame 321b; a guide shaft 328b, extending in the direction of the optical axis, slidably engaging the shaft bearing part 333b for guiding the lens frame 321b in the direction thereof.
The guide shaft 328a is held near a front end portion and a rear end portion of the guide shaft 328a by a hole portion 330a formed on a front wall 330f of a stationary frame 330 and by a hole portion 330a' formed on a middle wall 330m of the stationary member 330, so that the front end portion and the rear end portion of the guide shaft 328a slidably engage the stationary frame 330.
In the same way, the guide shaft 328b is held near a front end portion and a rear end portion of the guide shaft 328b by a hole portion 330b formed on the front wall 330f of the stationary frame 330 and by a hole portion 330b' (unshown in the figure) formed on the middle wall 330m of the stationary member 330, so that the front end portion and the rear end portion of the guide shaft 328b slidably engage the stationary frame 330.
Each of the shaft bearing parts 333a, 333b is equipped with a plate-spring-like holding plate 331a, 331b which is mounted thereto respectively with a screw (the holding plate 331b is hidden in the figure). The holding plates 331a, 331b make press connect with the guide shafts 328a, 328b, respectively. Therefore, when the lens frames 321a, 321b move on the guide shafts 328a, 328b, the shaft bearing parts 333a, 333b are slid thereon frictionally.
As shown in FIG. 25, the drive mechanism also has a pair of piezoelectric elements 325a, 325b that are mounted to the rear end portions of the guide shafts 328a, 328b. Rear end portions of the piezoelectric elements 325a, 325b are connected to fixing members 332a, 332b, respectively. These fixing members 332a, 332b are fixed to a rear end surface 330c of the stationary frame 330.
The principle of operation of a drive mechanism employing a piezoelectric element is briefly explained below with reference to schematic views shown in FIGS. 26(A), 26(B), 26(C).
As shown in FIG. 26(A), a driving shaft 353 is fixed to one end of a piezoelectric element 352, a fixing member 351 is fixed to the other end of the piezoelectric element 352, and a moving body 354 to be moved is held relative to the driving shaft 353 by a frictional force exerted by a spring for instance. The mass of the fixing member 351 is sufficiently large as compared with the mass of the moving body 354.
When a predetermined voltage is applied to the piezoelectric element 352, the piezoelectric element 352 is inhibited from expanding toward the fixing member 351 due to the force of inertia of the fixing member 351. Therefore the piezoelectric element 352 expands toward the driving shaft 353, causing the driving shaft 353 to be moved leftward in the figure.
In this operation, when the applied voltage is on a gentle rise as shown by part "A1" in FIG. 27, the moving body 354 moves together with the driving shaft 353 by a distance x because the frictional force exerting between the moving body 354 and the driving shaft 353 is larger than the force of inertia of the moving body 354, as shown in FIG. 26(B).
Next, when a voltage of an abrupt fall as shown by part "B1" in FIG. 27 is applied to the piezoelectric element 352, the force of inertia of the moving body 354 is larger than the frictional force exerting therebetween, while the piezoelectric element 352 is contracted. Therefore, at this time, the moving body 354 remains stationary, while only the driving shaft 353 contracts back to its original length so that it moves back by the same distance "x" to the original position, as shown in FIG. 26(C).
Applying a voltage with a sawtooth-shaped pulse waveform to the piezoelectric element 352 so that the aforementioned operation is repeated, allows the moving of body 354 to a desired position. By the way, in order to move the moving body 354 in a reverse direction, a voltage having an abrupt rise and a gentle fall is applied to the piezoelectric element 352.
The drive mechanism, as shown in FIG. 25, is actuated on a basis of the same principle of operation. That is, when a voltage with a predetermined sawtooth-shaped pulse waveform is applied repeatedly to the piezoelectric elements 325a, 325b for a specified time, the piezoelectric elements 325a, 325b expands and contracts so that the lens 300L1, 300L2 is moved toward a desired position, under a relation between the frictional force exerting between the guide shaft 328a, 328b and the holding plate 331a, 331b, and the force of inertia due to the mass of both the lens 300L1, 300L2 and the lens frame 321a, 321b.
However, in case that the drive mechanism is miniaturized with the miniaturization of the camera main body, the mass of the fixing member 332a, 332b is reduced; therefore, the force of inertia is also reduced. This may cause the fixing member 332a, 332b to move against the expansion and contraction of the piezoelectric elements 325a, 325b. That is, in case that the stationary frame 330 is made of an elastically deformable material such as plastic, the rear end surface 330c becomes easily flexible, so that this rear end surface 330c accompanies the movement of the fixing members 332a, 332b. In other words, in case that the stationary frame 330 is made of such an elastically deformable material, the rear end surface 330c has not enough rigidity not to allow the fixing member 332a, 332b to move.